Roller hemming is a production process for assembling closure panels made from either steel or an aluminum alloy sheet metal. Roller hemming uses a roller head typically as an end component on a robot that travels along a flange of one panel, gradually bending the flange over the edge of the other panel to form a roll hem. The assembly sequence typically includes application of a hem flange adhesive to the inside periphery of the outer panel, which is nested in a hemming anvil. An inner panel is placed in contact with the outer panel to marry the two panels. The outer panel flange is bent to create a roll hem over the peripheral edge of the inner panel. Depending on the type of adhesive used, it may be necessary to then move the assembly to an induction curing station to provide in-process dimensional stability of the closure by curing the adhesive. The assembly is then transferred to other work cells to undergo other processes in the plant. Finally, an after-hem sealer is applied (e.g., after the e-coat process). Seam welds are not used on hemmed closure panels in automotive applications, as the appearance of the surface of the panel at the seam weld would not be suitable for its purpose as a closure panel in an automotive body. Thus, the adhesive joins the panels, and the sealer is used to prevent water migration past the roll hem to the adhesive.
Ultrasonic welding is an industrial joining method that locally applies high frequency vibrations to work pieces held together under pressure to create a solid state weld. Such equipment has been used in production primarily for welding plastics and/or dissimilar metals. One application of ultrasonic welding can create a seam at the interface between two sheet metals in a lap joint configuration. Ultrasonic seam welding uses a rotating transducer attached to a roller tool that engages a top sheet, transfers high frequency vibration to the interface of a top and bottom sheet, respectively, resulting in a solid state weld joining the two sheets.